Have you thought about everything your skin has done for you today?

Perhaps you’re unhappy with your skin because it’s breaking out, or showing the signs of age, or sun damage. But are you aware of how hard your skin is working for you, all day, every day?

Skin is not superficial! It’s is your body’s largest organ—making up 16% of your physical weight. (The skin of a 150-pound person weighs about 24 pounds!) Laid out flat, your skin would measure approximately 22 square feet.

Your skin is literally your body’s front line of defense—protecting you from dehydration, temperature extremes, disease organisms, and environmental toxins. (Because your body is about 60 percent water, without your skin, you would literally evaporate.) A key part of your skin’s defense strategy is the microbiome it maintains of more than 1,000 types of bacteria. Most of these are “friendly” bacteria that help to heal wounds and battle inflammation.

Your skin is also your body’s largest sensory organ, conveying the sense of touch in all its variations: temperature, pressure, pain, itch, pleasure, and physical and chemical stimuli. Our skin is an important tool for “making sense” of the world.

In fact, your skin is the vital interface between your internal and external environments. It responds to both external and internal stimuli, sensing and integrating environmental cues, while simultaneously responding to and reflecting internal conditions. Our skin is so complex that researchers are just beginning to understand how the skin and skincare therapies affect internal health. Similarly, we are still unraveling how our internal systems affect our skin.

What we do know is that there is an elaborate web of interconnections, called the neuro-immuno-cutaneous-endocrine (NICE) system, which links nervous system, immune system, cutaneous (skin), and endocrine functions, all of which are important to physical, emotional, and mental health.

For example, disruption to the gut’s microbiome can cause various skin problems, including acne, eczema, rosacea, and more. Liver inflammation, anemia, and other conditions can cause jaundice—a yellowing of the skin and whites of the eyes. Jaundice can be accompanied by fatigue, abdominal pain, vomiting, weight loss, and fever. A healthy liver is the key to preventing jaundice, which means eating a balanced diet, exercising regularly, and avoiding excessive consumption of alcohol.

Our skin also reflects our emotional state. That’s why you might blush from embarrassment, turn red with anger, go white with fear, or get chills from the national anthem. Due to its close connection to our emotional state, it’s not surprising that our skin is profoundly affected by stress. In fact, trauma or severe stress can cause acne, hair loss, eczema or dermatitis flare-ups, herpes (oral and genital), hyperhidrosis (excess sweating), pruritus (itching), psoriasis (skin scaling and redness), rosacea (skin flushing and eruption), hives, and even warts. Stress also induces the release of cortisol, which triggers the production of enzymes that break down collagen. Collagen is the most common protein in the skin—it is literally the scaffolding that provides skin structure. So, when people ask me whether stress causes wrinkles, I say, “Absolutely!”

How well we treat our skin also affects our mental, emotional, and even physical health. The soothing experience of a facial has been shown to lower heart rate and blood pressure in addition to improving skin quality. As I’ve written previously, dry skin may contribute to a wide range of chronic, age-related conditions that include heart disease and Alzheimer’s.

(A pilot study by dermatologists at UC San Francisco has shown that topical moisturizers can reduce this risk factor by reducing the levels of three cytokines linked to age-related chronic diseases: interleukin-1 beta, interleukin-6 and tumor necrosis factor. Among seniors (ages 58-95) who moisturized twice daily, cytokine levels fell nearly to the level of people in their 30s. The moisturizers also lowered their skin’s acidity, improved hydration, and repaired its permeability.)

If you think of the skin as “superficial,” these results can strain credulity. But when you remember that the skin is your largest organ, you begin to see how caring for the skin means caring for the rest of your body, as well.

In my book, The Water Secret, I explain why “eating your water” and protecting your cellular hydration and cell membrane health internally are even more important than topical protections. Put them both together—and combine the two with a healthy outlook—and you have my optimal prescription for Modern Health and Wellness.

Now you know why I say that skin is the body’s “window to wellness” and Modern Wellness requires us to have NICE skin!